Postfix stable release 2.8.0

Postfix stable release 2.8.0 is available. This release continues
the move towards improving code and documentation, and making the
system better prepared for changes in the threat environment.

The postscreen daemon (a zombie blocker in front of Postfix)
is now included with the stable release. postscreen now supports
TLS and can log the rejected sender, recipient and helo information.
See the POSTSCREEN_README
file for recommended usage scenarios.

Support for DNS whitelisting (permit_rhswl_client), and
for pattern matching to filter the responses from DNS white/blacklist
servers (e.g.,
reject_rhsbl_client zen.spamhaus.org=127.0.0.[1..10]).